This invention relates to a system and method for interfacing a patient with equipment for monitoring the expired gas of said patient.
It is often necessary to monitor the condition of hospital patients closely and, typically, patients who require such attention may be found in the intensive care unit, recovery room, coronary care unit, operating room, or in general care areas.
These areas are normally provided with equipment which permits a few hospital personnel to monitor a relatively large number of patients at one time and some of such equipment may involve remotely located displays or measuring devices.
An example of such a system is one which monitors the expired gases of patients for the presence of CO.sub.2. A sharp reduction in CO.sub.2 for a particular patient could indicate an imminent failure of respiration, and, of course, absence of CO.sub.2 would indicate death of the patient. A sharp increase in CO.sub.2 could indicate another condition requiring attention.
Measurements of CO.sub.2, as well as other gases of interest, can be taken on a continuous basis by the use of a mass spectrometer, and for this purpose provision must be made for delivering continuously a sample of the expired gas to the measuring equipment. Unfortunately, the sampling process usually involves the presence of a certain amount of patient's secretions as well as natural and manufactured humidification which when reaching the mass spectrometer will affect the results. Attempts heretofore to filter out such liquids introduced levels of dead space into the interfacing system which affect adversely the accuracy of results produced by the mass spectrometer.
Another problem generally associated with such interfacing systems and methods has to do with patient comfort. In order to obtain the sample of exhaled breath, an endotracheal tube, nasal cannula, aerosol "T", or even a mask device may be employed, entering the patient either by way of the mouth and/or the nose or surgically through a tracheal incision. In order to hold the tube in place, extensive taping on the face and head of the patient is often required with resulting discomfort as a result of skin tearing and skin sores forming under the tapes. This problem is compounded when the tube has to be removed to permit moving of the patient, or some other procedure is to be performed followed by replacing of the tube and retaping. Also, burn patients can not be taped at all due to existing skin damage.
A variety of attempts have been made to overcome these problems. In U.S. Pat. No. 2,259,817 and 4,018,221 there are shown headbands for use with nasal cannula, but they do not appear to be useful with endotracheal tubes entering through the mouth. Also, it is believed that in these arrangements there is inadequate support where the tubes enter the nostrils. Also, no removal of patient secretions appears to be provided for in these patients.
In U.S. Pat. No. 4,060,074 there is a filter provided but only for removing solid particles from the gases being supplied to the patient. U.S. Pat. No. 4,090,513 shows an arrangement for humidifying the gas being inhaled. Other U.S. Patents of interest are U.S. Pat. Nos. 3,718,135 and 3,910,261, but these do not attempt to deal with the problems described above. Efforts have been made to employ cold traps to remove patient secretions and other liquids, but these have not been successful due to the excessively large dead spaces, in the order of 10-50 cc, which are added to the systems by such traps.